<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<!--<input type="button" value="红色" onclick="color()" id="op">
<input type="button" value="黄色" onclick="color()">
<input type="button" value="蓝色" onclick="color()">
<input type="button" value="自定义颜色" onclick="color()">-->
<input type="text" placeholder="圆的半径" id="a">
<input type="text" placeholder="圆的周长" id="b">
<input type="text" placeholder="圆的面积" id="c">
<script src="jj.js">

</script>
</body>
</html>